Resins have widespread use in today's manufacturing processes. When a material that incorporates a resin is manufactured, obtaining a desired degree of cure is a primary consideration. A completed cure will allow optimization of desired properties of the material, including hardness and strength. However, uncertainties regarding the characteristics of the materials involved and the thermodynamics of the manufacturing process complicates the curing process. Too long of a cure period can have an adverse impact on properties of the material and unnecessarily increase cost. Too short a period is also undesirable. The need for a control process is therefore manifest. An ideal cure control system should control the process regardless of the composition of the material.
A successful cure of polymeric materials, such as an epoxy resin, is accomplished when cross-linking occurs between the polymers. In most curable materials, this process involves reactions that absorb heat (endothermic) and that radiate heat (exothermic). A full cure is achieved when the amount of energy being applied to a material matches the amount of heat being radiated by that material. This equilibrium indicates that the endothermic and exothermic reactions have reached a steady state and the curing process is complete.
The curing requirements of a particular material can be represented by a cure profile. However, the profile will vary among different materials and even among batches of the same material. Most composite manufacturers attempt to create a cure profile to process their composites at optimum efficiency. One method of creating a cure profile involves destructive thermal analysis of a sample of a partially cured material. The sample is removed from the material during the cure process and is analyzed using techniques such as digital scanning calorimetry (DSC), thermomechanical analysis (TMA), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), or any other techniques well known it the art. These techniques involve multiple experiments and destruction of, or at a minimum contact with, the sample.
The use of destructive thermal analysis is ideally suited to a batch production process. A batch process involves the production of a specified quantity of material at one time. Sampling of the material for destructive thermal analysis is relatively simple because the curing procedure can be interrupted without an undue reduction in production. In contrast, a continuous production process involves continually producing material in a constant stream. In a continuous process, sampling is not feasible without halting the entire production stream.